body of research on Facebook, the questions, methods, and perspectives were so diverse and fragmented that it would be impossible to write a coherent summary of the literature. But we also realized that without summarizing the current trends in the literature—fragmented though they are—the situation was unlikely to improve. So we reviewed the literature and used it as the launching point for a broader examination of best-practice methods as well as a consideration of promising directions for future research. The current article is the result. As this article will show, there has been major progress toward analyzing behavior on Facebook and effectively

Overview: The major theme of Vygotsky's theoretical framework is that social interaction plays a fundamental role in the development of cognition. Vygotsky (1978) states: "Every function in the child's cultural development appears twice: first, on the social level, and later, on the individual level; first, between people (interpsychological) and then inside the child (intrapsychological). This applies equally to voluntary attention, to logical memory, and to the formation of concepts. All the higher functions originate as actual relationships between individuals." (p57). A second aspect of Vygotsky's theory is the idea that the potential for cognitive development depends upon the "zone of proximal development" (ZPD): a level of development attained when children engage in social behavior. Full development of the ZPD depends upon full social interaction. The range of skill that can be developed with adult guidance or peer collaboration exceeds what can be attained alone. Vygotsky's theory was an attempt to explain consciousness as the end product of socialization. For example, in the learning of language, our first utterances with peers or adults are for the purpose of communication but once mastered they become internalized and allow "inner speech". Vygotsky's theory is complementary to the work of Bandura on social learning and a key component of situated learning theory. Because Vygotsky's focus was on cognitive development, it is interesting to compare his views with those of Bruner and Piaget. This is a general theory of cognitive development. Most of the original work was done in the context of language learning in children (Vygotsky, 1962), although later applications of the framework have been broader (see Wertsch, 1985).

When observers tracked a horizontally moving spot, the path of a second spot moving at an angle to the horizontal was radically misperceived. At a signal observers abruptly switched to tracking the second spot, which was then stabilized foveally. Data concerning resulting eye movements and perceptions support a distinction between the “central” motor command, which is found to be formulated solely from the erroneous perception, and the motor command that finally reaches the eye, which, under some specifiable circumstances, has been “peripherally” transformed so that the actual motion of the eye is appropriate to the actual motion of the target.

A number of experiments were conducted to determine to what extent retinal image smearing during saccades provides information about the eye movement magnitude to the perceptual system. The technique involved obtaining measures of perceived movement when the total visual field was displaced in conjunction with saccadic eye movements. Trials with normal retinal smear were compared with trials on which smearing was greatly reduced or eliminated. The results are interpreted as showing that the absence of normal retinal smear during a saccade increases the uncertainty in the information available to the perceptual system and that this uncertainty results in a tendency to perceive smaller than veridical amounts of movement.

iReceived 2 February 1977; in re~ised~~~ IS .&far& 1977) The ability of observers to execute saccades in the dark to previously visible targets has been demonstrated by Becker and Fuchs (1969) and Becker and Klein (1973). Becker and Fuchs report the occurrence of horizontal saccades when a target, 40’ away from fixation. was extinguished 350 msec prior to the initiation of the saccade. Becker and Klein report that observers, after practicing horizontal saccades to targets were able to continue making goal-directed sac&es in total darkness. The accuracy of these saccades, however, decreased with time. These results imp1y that continuing retinal stimulation is not necessary for the execution of goal-directed saccades. Rather, the saccadic control system appears able to utilize some sort of stored information. The present experiment assessed the accuracy with which the saccadic control system could execute, from memory alone, a consecutive series of two-dimensional saccades to targets randomly located in the fronto-parallel plane.

Observers viewed a computer-generated display consisting of horizontally oriented, concave-up curved lines. The position of these curves was contingent on the horizontal position of the eye so that, in order to change fixation errorlessly, from one point to another on the curve, the eye would have to execute a purely horizontal movement. In Condition H this was achieved by moving the curves horizontally, so that the minimum point was always at the horizontal eye position location, thus simulating the effect of viewing a line through a wedge prism on a contact lens. In Condition V it was achieved by moving the curves vertically so that the point fixated always had the same vertical location. In both conditions eye movements were reprogrammed rapidly to eliminate the vertical components of the saccades that were present at the start. While a small, but significant, amount of perceptual adaptation was obtained in Condition H, none at all was obtained in Condition V. The results are interpreted as not in support of such theories of perceptual adaptation to curvature distortion as require a close relationship between motor learning and perceptual change.

With accurate measurement of eye position during smooth tracking, comparison of the retinal and perceived paths of spots of light moving in harmonic motion indicates little compensation for smooth pursuit eye movements by the perceptual system. The data suggest that during smooth pursuit, the perceptual system has access to information about direction of tracking, and assumes a relatively low speed, almost irrespective of the actual speed of the eye. It appears, then, that the specification of innervation to the extraocular muscles for smooth tracking is predominantly peripheral, i.e. it occurs beyond the stage in the efferent command process monitored by perception.

have been addressed.The problems, issues, and current state of the work is well presented by Evarts, Bizzi, Burke, DeLong, and Thach (1971).However, there has been little or no work that addresses questions about the efferent system from a psychophysical point of view.There have been studies that have shown the importance of the efferent system in enabling adaptation to distorted visual input (Festinger, Burnham, Ono, & Bamber, 1967;Held, 1961) but this work only implicates the efferent system-it does not explicate it.We think that it is possible to make progress in understanding the nature and functioning of the efferent system through psychophysical methods.It is the purpose of this article to propose a paradigm for doing this, to present the results of a study following this paradigm, and to present the beginnings of a theoretical model, necessarily narrow in scope, that suggests itself as a result of these findings. AN APPROACH TO THE STUDY OF THEEFFERENT SYSTEM Some aspects of visual perception are particularly well suited for analyzing what happens in the efferent system.This suitability arises from the fact that the perceptual system does not have access to information about eye movements or eye position based on proprioceptive feedback from the extra-

Early in twentieth century, a new approach to understanding of visual perception began to develop. This approach stressed importance of relations among parts of visual field and insisted that percept could not be explained in terms of elements impinging on retina. This is point inherent in writings of von Ehrenfels (1890) on 'Gestaltqualitat,' in early work of Wertheimer on phi phenomenon (1912), in formulation by Koffka (1935) of principles of organization of visual world, and in many demonstrations produced by 'Gestalt psychology.' The essence of point has been summed up in often quoted, and sometimes misquoted, statement that the whole is different from sum of its parts.

Eye movements, made in response to a target that was displaced twice (pulse-step stimuli), were recorded for three observers in order to ascertain the characteristics of the saccadic control system. Five types of pulse-step stimuli were randomly presented to the observers. The results indicate that observers did not always respond to the initial displacement of the target, but sometimes responded only to the target's final position. The percentage of instances in which observers responded to the pulse increased as the duration of the pulse increased from 50 to 200 msec. In those instances when observers responded to both target displacements, the latency of the second saccade was shorter than that of the first. When observera only responded to the target's final position, the latency of the saccade was shorter if the target's final position was in the same direction than if it was in the opposite direction from its initial displacement. These results suggest that there is continuous input of information into the saccadic control system.

A series of experiments demonstrated that the flicker colors can be produced by appropriate changes in the intensity of a stationary light source. If the intensity changes resemble those produced by a Benham Top, then lateral inhibitory effects from a flickering background must be present to produce the colors. Patterns of temporal intensity changes were discovered by means of which the flicker colors were produced with a constant background.